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Research Notes

Removing difficult pollutants from wastewater

Researchers
at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB
(Stuttgart, Germany) have found that oxidative processes with hydrogen peroxide
or ozone are effective at removing persistent pollutants from wastewater. Water
resource recovery facilities’ biological treatment processes often are unable
to remove such pollutants as drugs and cyanides, and additional special
treatment is required, according to a Fraunhofer Institute news release.

The
institute runs a pilot facility in Stuttgart to test standard processes to
determine how best to degrade many different components in wastewater. Two new
methods have efficiently generated reactive species, especially hydroxyl radicals.
These radicals oxidize pollutants into smaller, more degradable organic
molecules or mineralize them completely to carbon dioxide.

The first
method is an electrochemical oxidative process that does not require additives
and is suitable for treating extremely turbid wastewaters, the news release
says. Developed within the CleanLeachate project funded by the European Union,
it generates hydroxyl radicals when voltage is applied in a combined
anode–cathode process. A membrane separates an electrolytic cell into two
separate chemical-reaction areas. Polluted water flows past the anode, where it
is oxidized and then pumped to the cathode, where the components are reduced,
the news release says. A consortium of six partners from five European countries
is using this process to treat highly polluted leachate from landfill sites.

The
second method is an atmospheric-pressure plasma reactor that purifies water
during an oxidative process. Plasma, an ionized gas, can be ignited by applying
high voltage. A stainless steel cylinder inside the reactor acts as a grounded
electrode, and a copper network acts as a high-voltage electrode. The copper
network sits on a glass cylinder, which acts as a dielectrical barrier,
shielding the reactor to the outside. When high voltage is applied, plasma is
ignited and maintained between the cylinder and copper network. Polluted water
is pumped through the cylinder, and as water flows down the outer surface of
the cylinder, it passes through the plasma zone, where pollutants are oxidized,
the news release says. The method, funded by the European Union, is being
applied by partners of a joint water plasma project. Researchers have been able
to break down cyanide with this method. The method now is being tested on a
larger scale, the news release says.

Researchers
also determined that an absorption stage is effective when pollutants are
strongly diluted, present in low concentrations, or highly specific, the news
release says. They developed a single-stage, cost-effective process for
producing polymer adsorber particles. In the institute’s patented process,
Nanocytes®, functional monomers are transformed into small polymeric
adsorber particles with a cross-linking agent. The selectivity of the adsorber
particles can be increased by adding to the mixture the target molecules to be
removed from the water. Once monomers have been polymerized, target molecules
can be removed from the adsorber particles. The approach offers flexibility in
the design of surface chemical properties and adsorption behavior. And once the
pollutants have been adsorbed, the adsorber particles can be regenerated and
reused, the news release says. Researchers have been able to remove bisphenol A
and penicillin G selectively from wastewater.

September
WER examines runoff from permeable pavement

While runoff from
newly constructed porous pavement contains fewer contaminants than other
pavement, this does not always translate to improvement in the quality runoff
quality over time. But stormwater treatment can improve the water quality of
runoff, according to researchers from the National Institute of Water and
Atmospheric Research (Newmarket, New Zealand).

Researchers collected
samples from four sites in Auckland, New Zealand; two were from impervious
roads, and two from roads paved porous friction course (PFC).

The research,
reported in the September issue of Water Environment Research (WER),
found that while runoff from a 1-year-old PFC highway was better than runoff
from other sites, runoff from a 6-year-old PFC highway was similar in quality
to that discharged from impermeable roads. The deterioration of runoff quality
is consistent with the clogging of spaces in porous concrete and decrease in
its permeability, the report says.

Researchers also
collected runoff samples at the outlet of a grass swale at the 1-year-old PFC
highway and a wet pond at the 6-year-old PFC highway. Both showed reductions in
contaminants, with the former predominantly lowering dissolved metal
concentrations and the latter lowering particulate metal concentrations.

“These results
indicate that stormwater treatment can improve the quality of runoff discharged
from PFCs, irrespective of their age, provided that treatment is targeted to
the predominant contaminant phase present,” the report says.

The article,
“Variations in Highway Stormwater Runoff Quality and Stormwater Treatment
Performance in Relation to the Age of Porous Friction Courses,” is available as
an open-access document and can be downloaded free at http://goo.gl/Ao7Yqf.

Water
Environment Research allows open access to one article per issue on a range
of important technical topics such as nutrient removal, stormwater, and
biosolids recycling.